As is disclosed in U.S. Pat. No. 4,213,590 granted July 22, 1980, a trailer hitch head includes a pair of movable jaws to hold in place a king pin of a highway trailer. The jaws are held in closed position by a lock block which is biased to closed position by a stiff spring. The lock block is movable manually to open position by an operating shaft extending to a side of the hitch which can be actuated to move the lock block rearwardly against the bias of the spring to hold it there by means of overcenter geometry, to allow the jaws to pivot to open position under the action of the king pin. This pivoting action then trips the geometry back overcenter so the jaws are ready to resecure the next king pin. This hitch is not retractable. The king pin securement can only be manually actuated.
In U.S. Pat. No. 4,230,431, a trailer hitch is disclosed including a vertical strut and a diagonal strut. The hitch is automatically movable to a retracted position on the deck of a transportation vehicle when a tractor engages a bumper block which is connected to a linkage in the diagonal strut which disengages at least one movable lug from engagement with a fixed lug on the deck to allow the hitch to assume a retracted position.
In this construction the diagonal strut includes a transverse bar adjacent the hitch head which strikes a pivoted finger on the head to move a lock block rearwardly to allow the jaws to move to open position.
In this construction the need for manually moving the lock block to open position and holding it there was accomplished by a secondary mechanism which had to be simultaneously engaged while rotating the operating shaft.
For manual operation, the shaft could not be extended to the side of the hitch to form a handle because in retracted position the shaft would interfere with the diagonal strut and require the operator to furnish a handle. Therefore in U.S. Pat. No. 4,333,666 issued June 8, 1982, the shaft was moved up higher in the hitch head to avoid interference with the diagonal strut, and was extended to the side of the head and formed into a handle for manual operation. This necessitated changing the direction of rotation of the operating shaft to move the lock block back. This design was for manual operation only.
However, some customers have desired a hitch of this later type in which when the bumper bar is engaged by the tractor to move the hitch to retracted position, the jaws would automatically be allowed to open.
Some customers also have a desire for a hitch capable of both manual and automatic operation.